Fix ambiguous matches for -N and -L and set default optimzer sgd.
Fix ambiguous matches for -N and -L and set default optimzer sgd.

lezorich/mlpack,datachand/mlpack,theranger/mlpack,thirdwing/mlpack,ersanliqiao/mlpack,Azizou/mlpack,ajjl/mlpack,datachand/mlpack,ranjan1990/mlpack,darcyliu/mlpack,bmswgnp/mlpack,minhpqn/mlpack,stereomatchingkiss/mlpack,thirdwing/mlpack,ersanliqiao/mlpack,palashahuja/mlpack,trungda/mlpack,erubboli/mlpack,BookChan/mlpack,theranger/mlpack,lezorich/mlpack,BookChan/mlpack,erubboli/mlpack,ajjl/mlpack,lezorich/mlpack,minhpqn/mlpack,bmswgnp/mlpack,minhpqn/mlpack,ranjan1990/mlpack,trungda/mlpack,ranjan1990/mlpack,BookChan/mlpack,chenmoshushi/mlpack,theranger/mlpack,Azizou/mlpack,trungda/mlpack,erubboli/mlpack,darcyliu/mlpack,palashahuja/mlpack,stereomatchingkiss/mlpack,chenmoshushi/mlpack,thirdwing/mlpack,Azizou/mlpack,bmswgnp/mlpack,ersanliqiao/mlpack,chenmoshushi/mlpack,datachand/mlpack,darcyliu/mlpack,palashahuja/mlpack,stereomatchingkiss/mlpack,ajjl/mlpack